This invention relates to a continuous atmosphere furnace which is employed for the heat treatment of metallic articles in a specific atmosphere. And, more particularly, it relates to agitator means utilized in such continuous atmosphere furnace for promoting the reformation of its specific atmosphere.
Heretofore, the formation or reformation of a furnace atmosphere to a desired composition has been made generally by mixing an additive gas into the furnace atmosphere.
In this instance, the additive gas introduced into the furnace can act to reform the existing furnace atmosphere by its reaction with the furnace atmosphere only when the additive gas is heated and mixed well with the furnace atmosphere. Therefore, if the additive gas is not properly introduced into the furnace, that is, without due consideration of its relation with articles to be treated in the furnace, the atmosphere will come into contact with the articles before it has been reformed substantially completely. Poor reformation of the furnace atmosphere will often result in poor or inadequate heat-treatment of articles in the furnace.
In this context, reference is made to U.S. Pat. No. 4,292,436 of this inventor. In the furnace for the heat-treatment of metallic articles with a protective atmosphere which is disclosed in said U.S. Patent, a substantial part of raw gases supplied into the furnace will disadvantageously make contact with metallic articles to be heat-treated before they make contact with catalytic and heating means and are reformed into a disired composition, although fans intend to agitate the raw gases radially before they make contact with the metallic articles.
Reference is further made to Japanese Preliminary Patent Publication No. 54-64633 which discloses a carburizing furnace, into which the constituents for producing the desired atmosphere are supplied dropwise. In this furnace, a gas agitator is rotated within a space, lateral sides of which are encircled by wire gauzes containing a catalyst, and bottom side of which is closed by an upper plate of a muffle. Although this muffle prevents the incoming constituents to drop directly over articles to be heat-treated, it also prevents the existing furnace atmosphere from passing upwardly into the space where the gas agitator is rotated. This means that it can hardly be expected that the incoming atmosphere constituents falling dropwise into the space will be mixed there with the furnace atmosphere and reacted by the gas agitator. In other words, this gas agitator acts primarily as an atomizer which is vigorously rotated so as to atomize the incoming atmosphere constituents and radially and forcibly disperse them as soon as they are dropped into the agitator space. It acts therefore little as an agitator.
It is further disadvantageous in this type of carburizing furnace that since a dropper pipe is to be provided and opened between the circular catalyst and the agitator and adjacently to a rotary path of vanes of the gas agitator so that the incoming constituents falling down from the dropper shall be atomized in an instant by wind current of the agitator, it is impossible to locate the circular catalyst very closely to the agitator on account of the above-mentioned interposition of the liquid dropper between them.